Wheel balancers, in general, comprise a housing which rotatably carries a substantially horizontal main shaft on which a wheel to be balanced is rigidly mounted by suitable coupling means. The main shaft is rotatable in bearings which, in general, are mounted or suspended from the housing so that transducers may be mounted between the bearings and the housing to enable out of balance moments in the main shaft to be detected. In practice, a wheel to be balanced is rigidly coupled to the main shaft and rotated at a speed sufficient that any imbalance in the wheel induces an out of balance moment in the main shaft sufficient to be detected by the transducers. Electronic signals from the transducers feed suitable electronic analyzing circuitry which computes the value and direction of the imbalance forces, and in turn, computes and displays the value of balance weights required and their relative positions on the wheel to correct the imbalance. In slow speed balancers, generally of the type which require rotation of the main shaft by hand, it is generally necessary to rotate the main shaft to a speed of at least 50 revs per minute, and usually, to a speed not exceeding 180 revs per minute. Typically, slow speed manual wheel balancers require rotation of the main shaft at approximately 70 to 150 revs per minute. In high speed balancers, generally of the type in which the main shaft is motor driven, the main shaft is typically rotated at a speed of the order of 300 revs per minute or greater.
To permit accurate computation of the imbalance of the wheel, it is essential that the wheel, when mounted on the main shaft, should be mounted and aligned co-axially with the main shaft. Otherwise, the results computed by the wheel balancer will be inaccurate. A wheel which is not co-axially aligned with the main shaft will yield an out of balance moment when rotated irrespective of whether the wheel is allegedly balanced or otherwise. The out of balance moment is further accentuated by the effects of gravity. In general, light weight wheels may readily easily be coupled manually on the main shaft of a wheel balancer by merely lifting the wheel onto the main shaft, and, by using a suitable coupler on the main shaft, the wheel can be co-axially aligned with the main shaft without any great difficulty. However, considerable difficulty is encountered where it is necessary to couple a relatively heavy or large size wheel onto the main shaft, such as, for example, a wheel of the type which would normally be used on a light weight truck such as, for example, a pick-up truck, van or other such vehicle. Needless to say, the heavier the wheel, the greater is the chance of the wheel being misaligned on the main shaft. The difficulty in centring the wheel on the main shaft to avoid misalignment arises from the fact that the wheel firstly, has to be lifted on to the main shaft, and then has to be lifted once more onto a coupling mechanism on the main shaft for coupling the wheel to the main shaft. In general, the coupling mechanism comprises a conical centring device, and the wheel has to be lifted onto the conical centring device for alignment with the main shaft. To do this, it is necessary to hold the wheel with one hand while a clamping device, generally, a nut on the main shaft is tightened with the other hand for securing the wheel to the coupling mechanism. It will be appreciated that where a relatively heavy wheel is to be coupled to the main shaft a considerable strain is applied to the back of the individual who is coupling the wheel to the main shaft.
Furthermore, due to the effects of gravity accurate centring of the wheel on the main shaft is difficult, and in some cases impossible, thereby leading to misalignment of the wheel with the main shaft.
In many cases to overcome these problems, mechanical lifting apparatus is used for lifting the wheel onto the main shaft, and for holding the wheel substantially aligned with the main shaft until the wheel has been securely coupled to the main shaft. Alternatively, two operators may be required, one to hold the wheel in position on the conical centring device while the other operator tightens the nut on the main shaft to secure the wheel to the coupling mechanism and in turn to the main shaft. This, it will be appreciated, is unsatisfactory, and furthermore, where such heavy wheels are not co-axially aligned with the main shaft, spurious results are obtained. This, needless to say, requires subsequent re-balancing of the wheel.
Furthermore, where an operator is fatigued when carrying out a wheel balancing operation, as a result of having balanced many wheels, or for other reasons, it has been found that even with relatively light weight wheels a fatigued operator may couple a relatively light weight wheel onto a main shaft of a wheel balancer with the axis of the wheel to be balanced, and the main shaft misaligned.
U.S. Pat. No. 3,922,922 discloses a wheel balancer which attempts to overcome these problems. Briefly, the wheel balancer of the U.S. specification comprises a cabinet within which a shaft support housing for rotatably carrying a main shaft is mounted. A wheel to be balanced is coupled to the main shaft. Suitable transducers co-operating with the main shaft and the shaft support housing enable imbalanced forces in the wheel to be detected on rotation of the wheel and main shaft. The shaft support housing is suspended by a bracket from a horizontal pivot axis, and a double acting hydraulic ram connected between the cabinet and the shaft support housing pivots the shaft support housing from a horizontal to a vertical position to facilitate coupling of the wheel. Unfortunately, this wheel balancer of U.S. Pat. No. 3,922,922 suffers from a number of serious disadvantages. It is particularly cumbersome and awkward to use, and is also relatively slow to use. It is also prone to mechanical failure, hydraulic leaks and the like. Because the shaft support housing is pivoted by a double acting hydraulic ram, operation of the balancer is considerably slowed down, which needless to say, leads to inefficiency of use. In order to couple a wheel to the main shaft according to the description in the U.S. specification, the shaft support housing should first be pivoted into the vertical position. The wheel must be lifted from the ground onto the main shaft and coupled thereto. This requires considerable operator effort, and is not feasible in the case of heavy or cumbersome wheels. Furthermore, in order to pivot the main support housing in the first instance from the horizontal to the vertical position, an operator must first operate appropriate hydraulic valves and operating levers for operating the hydraulic ram for pivoting the shaft support housing. This is a relatively slow, tedious and time-consuming operation, and thus reduces the efficiency of the wheel balancer. Even if one were to first lift the wheel to be balanced from the ground onto the main shaft with the shaft support housing in the horizontal position, the operation of appropriate hydraulic valves and operating levers by the operator would still be required in order to cause the hydraulic ram to pivot the shaft support housing from the horizontal to the vertical position. As discussed above, this is a relatively slow and tedious and inefficient operation. On the shaft support housing being in the vertical position, the wheel would be coupled to the main shaft. To balance a wheel, if the wheel is to be balanced with its rotational axis horizontal, it is then necessary to operate the operating levers controlling the hydraulic ram to operate the ram for pivoting the shaft support housing from the vertical to the horizontal position. Again, this is a relatively slow and tedious operation. A further disadvantage of the device of U.S. Pat. No. 3,922,922 is that the hydraulic ram needs some form of supplied energy, such as electricity powering, an electric motor, which powers an hydraulic pump to supply pressure to the hydraulic ram. This, needless to say, further adds to the cost and complexity of the device, and increases the likelihood of component failure, hydraulic oil leaks and the like resulting in consequential down time of the wheel balancer. Furthermore, because of the construction of the wheel balancer of U.S. Pat. No. 3,922,922, it would not be feasible to operate the balancer without the hydraulic ram since the hydraulic ram as well as being required for pivoting the shaft support housing, the hydraulic ram is also required for retaining the shaft support housing in the respective vertical and horizontal positions.
There is therefore a need for a wheel balancer and a method for rigidly coupling a wheel to be balanced in co-axial alignment with a main shaft of the wheel balancer which overcomes the problems of the wheel balancer of U.S. Pat. No. 3,922,922 as well as other prior art wheel balancers.